Facility for reducing metal oxide, method for operating the facilities and moldings as law material to be charged to reduction furnace

ABSTRACT

The present invention provides a reducing furnace of the rotary hearth-type and a method for reducing a metal oxide simplified in the process from dehydration to molding, according to which a moisture-rich powdery raw material is reduced at low cost. The present invention also provides an operation method whereby dusts or sludge generated in the refining or processing of metal are economically recycled.  
     A powdery mixture having a moisture content of 100% or higher relative to the total mass of a metal oxide-containing powder and a carbon-containing powder is made into a slurry and mixed by stirring. Thereafter, the slurry is dehydrated to a moisture content of 16 to 26% and compression-molded into articles. The cylindrical or granular shaped articles having a thickness or diameter of 30 mm or less thus obtained are fed to a zone the atmospheric temperature of which is 1170° C. or lower in the furnace and reduced through calcination by a rotary hearth reducing furnace thereby to provide a metal.

TECHNICAL FIELD

[0001] The present invention relates to a facility for reducing metaloxides, a rotary hearth reducing furnace which is the facility mentionedabove, a method for reducing a metal oxide using the same, and to amethod for reducing metal oxide-containing dusts and sludge generated bythe metal refining or processing industry.

BACKGROUND TECHNOLOGY

[0002] There have been proposed a variety of processes for producingreduced iron or an iron alloy. Of these, there is one known as a processof high productivity that that includes the use of a rotary hearthreducing furnace, with which the reduction of a metal is effected. Theessential part of this process is the use of a rotary hearth reducingfurnace for reducing a metal oxide, the furnace being a firing furnaceof the type in which, under a fixed fire resistant ceiling and sidewalls, a center-lacking-disk-shaped fire resistant hearth rotates alonga rail at a constant speed (hereafter, referred to as a rotary furnace).Generally, the diameter of the disk-shaped hearth is from 10 meters to50 meters, and its width is 2 meters to 6 meters.

[0003] After having been mixed with a carbon-based reducing agent, ametal oxide-containing powder as a raw material is pelletized to makeraw material pellets and fed to the rotary hearth. The raw materialpellets are spread all over the hearth. Since the raw material pelletsare held stationary in relation to the hearth, this process has theadvantage that the raw material pellets are hardly broken up in thefurnace and therefore it is free from the problem of the raw materialbreaking up to form a powder which sticks to the fire resistant hearth.Moreover, this process has the advantage of high agglomerate productionyield. Furthermore, since its productivity is high and a less expensivecoal-based reducing agent and powdered raw materials can be employed, inrecent years, the number of cases employing this method are increasing.

[0004] The rotary hearth method is also effective in reducing dustsgenerated through the process of steel manufacture in blast furnaces,basic oxygen furnaces, and electric arc furnaces, and in reducingthickener sludge generated in a rolling step, and in removing impuritiestherefrom. This method has been adopted for treating dusts and iseffective in recycling materials.

[0005] How the rotary hearth method is carried out is described below inoutline. Firstly, after metal oxides such as ores, dusts, or sludge as araw material are mixed with a certain amount

[0006] of a carbon-based reducing agent required for the reduction ofthe oxides, the resulting mixture is granulated into pellets of fromseveral millimeters to several tens of millimeters by a granulator suchas a pan pelletizer while supplied with water so as to have an averagemoisture content of approximately 10%. In the case where the particlesize of an ore as the raw material or that of the reducing agent islarge, after having been crushed by a pulverizer such as a ball mill,the materials are kneaded and granulated.

[0007] The pellets thus obtained are fed onto the hearth of a rotaryfurnace in layers. The pellets spread all over the hearth are quicklyheated and calcined at temperatures as high as 1100 to 1300° C. for 5 to20 minutes, whereby the metal oxide is reduced by the reducing agentmixed in with the pellets to provide a metal. Depending on what kind ofmetal is to be reduced, the degree of metallization varies. In the caseof iron, nickel, or manganese, the degree of metallization reaches 95%or higher. Even if the metal to be reduced is chromium, the reduction ofwhich is difficult, the degree of metallization reaches or exceeds 50%.Moreover, in the case of treating dusts generated by the steelmanufacturing industry, their recirculation back to a blast or electricarc furnace is easy, because such impurities as zinc, lead, alkalinemetals, and chlorine are volatilized as the reduction reaction proceeds.

[0008] As described above, in the method for reducing metal or dustsgenerated in the process of steel manufacture through the use of arotary hearth, it is necessary to pelletize the raw material and thereducing agent. It is also essential that, as a pretreatment of the rawmaterials, the mixture of a powdered metal oxide and a reducing agent asthe raw material be brought into a condition suitable for granulation.As the pretreatment, milling of the raw materials, kneading with a ballmill, or any of a variety of techniques are carried out.

DISCLOSURE OF THE INVENTION

[0009] As described above, the reduction of a metal oxide with the useof a rotary hearth method using a conventional method is excellent withrespect to productivity or production cost, so that a metal is producedeconomically. However, in the prior art, it was important to mix a rawmaterial and a reducing agent and then pelletize the resulting mixture.Therefore, it was necessary to employ a material of high granularity orto install an expensive pulverizer in the production line for crushingthe raw material to improve its granularity. This resulted in a rise inthe production cost.

[0010] In other words, when an ore such as iron ore was employed as theraw material, due to its large particle size, it was in many casesgranulated to form pellets after having been milled so as to have anaverage particle size of about several tens to a hundred microns. Thisinvolved the use of a costly device for crushing, electricity to drivethe pulverizer, and the maintenance costs due to the wear of thepulverizer.

[0011] In some cases, a microfine powder raw material was employed forsaving the cost of milling. However, due to the strict limitations on,e.g., particle size in the selection of the raw material, such a methodwas not in wide use. For solving such problem, the use of awet-beneficiated powdery ore or thickener dusts generated in a blastfurnace or basic oxygen furnace, scale pit sludge produced in therolling step, or sedimentary sludge generated in the acid cleaning stepis effective. However, even in this case, there was a problem that themoisture content of such raw materials was so high that it was hard togranulate them. In other words, since these raw materials are finelydivided powders each having a particle size of from about 1 micron orless up to a hundred microns and thus liable to be sludgy whenmoisturized, even if dehydrated by a vacuum dehydrator or filterpresser, their moisture content cannot be lower than 20 to 50%. Themoisture content of the raw material upon pelletization is suitablyabout 8 to 13% by mass and therefore these raw materials collectedaccording to the wet process were too moist to be granulated as theywere.

[0012] One way to solve such problems as described above is tocompletely dry these raw materials using a heat source such as hot air.However, since these powdery raw materials are quasi-coagulated in thedrying step and thus unable to be granulated as they are, after havingbeen brought back into a micro-powdery condition again through milling,they were hydrated together with, for example, coke breeze, granulated,and reduced on the rotary hearth.

[0013] Accordingly, in the case of utilizing any of these raw materialscollected by the wet process in such manner as described above, afterdrying with a large amount of heating energy, the material is moistenedagain and evaporation of moisture upon granulation entails the use of aheat source again. This is not at all economical as a method forreducing metal.

[0014] Especially, dusts or sludge generated by the metal refining orprocessing industry exemplified by the steel industry and collected fromwet dust collectors or sedimentation tanks have, at a maximum, amoisture content of 80%. Attempts at reducing them in accordance withthe rotary hearth method were faced with problems related to thetreatment in the drying step and the milling or crushing step afterdrying.

[0015] For solving these problems, for example, as recited in JapanesePatent Laid-Open Publication No. Hei. 11-12619, there has been proposeda method including using a raw material in a rotary hearth-type reducingfurnace without granulation, in which the raw material is shaped in theform of tiles by a compression molding machine and the resulting tilesare used in the rotary hearth reducing furnace. However, even in thismethod, the use of a raw material containing a large amount of moisturehad problems. That is, the method disclosed by Japanese Patent Laid-OpenPublication No. Hei. 11-12624 also required the moisture content of araw material in the form of tiles to be adjusted to 6 to 18%. When amicrofine powder of about hundred microns was in a wet condition,dehydration by an ordinary dehydrator enabled the moisture content to bereduced to no lower than 15 to 30% by mass. In other words, this methodalso requires the raw material to be dried in addition to dehydrationprior to the reduction, resulting in the necessity for complicatedmoisture control to which an increase in the cost of equipment thereforeis a contingency.

[0016] Furthermore, as raw materials in the form of tiles are difficultto handle, when transported by an ordinary belt conveyer, conveyancerelated problems such as their breaking into pieces in transit mayoccur. That is, almost all tile-shaped raw materials, the water contentof which is 6 to 18%, are damaged by a fall of about 0.5 to 1 meter. Asa result, as described in Japanese Patent Laid-Open Publication No. Hei.11-12621, a complicated feeding device was necessary for softly placingthese tiles in the furnace, which presented problems typified by anincrease in investment cost.

[0017] As described above, for reducing a water containing powdery rawmaterial in a rotary hearth, the conventional method entailed a lot ofcomplicated devices for drying or shaping the raw material and thus hada problem of a high construction cost. In other words, the conventionalmethod had economical problems related to both plant investment andoperation cost, and a facility which realizes a novel method capable ofsolving these problems has been demanded.

[0018] Furthermore, by providing such a complicated feeding device inthe vicinity of a high temperature zone of 1000° C. or higher, thecomponents of the feeding device were distorted by heat or corrodedunder high temperatures, and there were many maintenance relatedproblems.

[0019] In addition, wet raw materials in the form of tiles have aproblem with respect to their tendency towards explosive-cracking.Although they are less explosive than pellets, yet those with a highmoisture content of 12 to 18% by mass such as described in JapanesePatent Laid-Open Publication No. Hei. 11-12621 tend to explode easily.This is because, if the raw material is in the form of tiles, watervapor does not move in a lateral direction. In other words, if the rawmaterial is in the form of tiles, due to their length being extremelylong in a lateral direction spatially, water vapor is discharged only ina vertical direction, causing a rise in passage resistance to facilitatetheir explosive-cracking.

[0020] As described above, a method according to which the reduction iseffected through calcination by a rotary hearth without drying amoisture-rich powdery raw material is desirable. However, in the furnaceheated to high temperatures, moisture is violently vaporized frommoisture-rich shaped articles to cause explosive cracking of thearticles. As a result, the shaped articles are powdered, leading to alarge increase in the amount of dust exhausted together with exhaust gasand an extreme decrease in agglomerate production yield. That is, adirect calcination-reduction of shaped articles having a relatively highmoisture content according to a conventional method was not economical.

[0021] As described above, every conventional method described above haseconomical problems in reducing a water containing powdery raw materialby a rotary hearth, and a novel technique for solving such problems hasbeen demanded.

[0022] The present invention will be described below with the numbers(1) to (25).

[0023] (1) A facility for reducing a metal oxide which is characterizedby including: a compression molding machine for shaping the mixture of awater containing powder containing a metal oxide and a powder containingcarbon into a cylindrical or granular shaped article; a shaped articletransporting conveyer; a shaped article feeding device; and a rotaryhearth reducing furnace, wherein the aforementioned devices are placedin this order and connected to each other by transporting means.

[0024] (2) A facility for reducing a metal oxide which is characterizedby including: a device for mixing a powder containing a metal oxide anda carbon-based powder in a water containing condition; a slurrytransporting device; a dehydrator; a compression molding machine forproducing a cylindrical or granular shaped article; a shaped articletransporting conveyer; a shaped article feeding device; and a rotaryhearth reducing furnace, wherein the aforementioned devices are placedin this order and connected to each other by transporting means.

[0025] (3) The facility for reducing a metal oxide according to (2)which is characterized by using, as the dehydrator, a dehydrator havinga belt-like filter for receiving the mixture of a metal oxide-containingpowder and a carbon-based powder in a water containing condition andtwin rolls between which the filter is sandwiched and compressed.

[0026] (4) The facility for reducing a metal oxide according to (2)which is characterized by using, as the dehydrator, a centrifugaldehydrator having a vertically cylindrical slurry holder a bottom ofwhich is tapered inward and a screw-type powder discharge mechanismprovided inside the holder, wherein the difference in rotation ratebetween the slurry holder and the powder discharge mechanism is 2 to 30rotations per minute, and the centrifugal force exerted on the slurryholder is 500G or more.

[0027] (5) The facility for reducing a metal oxide according to (2)which is characterized by using, as the dehydrator, a dehydrator havinga device for, from both sides, pressing a filter for receiving themixture of the powder containing the metal oxide and the powdercontaining carbon in a water containing condition with a force of10⁶N/m² or more.

[0028] (6) The facility for reducing a metal oxide according to (1) or(2) which is characterized by using, as the molding machine, acompression molding machine of a type which extrudes a wet powder fromholes each having a diameter of 30 mm or less.

[0029] (7) The facility for reducing a metal oxide according to (1) or(2) which is characterized by using, as the molding machine, a briquettemolding machine a maximum thickness of each concavity of which is 30 mmor less.

[0030] (8) The facility for reducing a metal oxide according to (1) or(2) which is characterized in that in the course of transportation froma shaped article manufacturing machine to a hearth of a rotary furnace,a total drop distance of the shaped article is 4.1 m or less.

[0031] (9) The facility for reducing a metal oxide according to (1) or(2) which is characterized by using, as the shaped article feedingdevice, a swing-type belt conveyer.

[0032] (10) The facility for reducing a metal oxide according to claim 2which is characterized in that the powder containing the metal oxide andthe carbon-based powder are supplied to the device for mixing from aplurality of tanks storing water-containing powders by a grab bucketcrane and/or slurry transportation in such a condition as to have amoisture content of 100% or higher relative to the total mass of thepowders.

[0033] (11) The facility for reducing a metal oxide according to (1) or(2) which is characterized by including a mechanism for controlling anatmospheric temperature of a shaped article supplying zone in the rotaryhearth reducing furnace so as to be 1170° C. or lower.

[0034] (12) A method of operating a rotary hearth reducing furnace whichis characterized by including dehydrating a powdery mixture containing ametal oxide, carbon, and water to a moisture content of 15 to 30% bymass relative to the whole mixture, shaping the mixture into a pluralityof cylindrical or granular shaped articles by compression molding, anddirectly feeding the shaped articles to the reducing furnace forreducing through calcination.

[0035] (13) A method of operating a rotary hearth reducing furnace whichis characterized by feeding a shaped article having a powder fillingrate of 0.43 to 0.58 produced by mixing a powder containing metal oxideand carbon in such a condition as to have a moisture content of 100% orhigher relative to the total powder mass, dehydrating it by a dehydratorto a moisture content of 16 to 26% by mass, and shaping it by acompression molding machine to a zone in the furnace an atmospherictemperature at which is 1170° C. or lower, and then reducing the shapedarticle through calcination at temperatures of 1200° C. or higher.

[0036] (14) The method of operating a rotary hearth reducing furnaceaccording to(12) or(13) which is characterized by using, as thedehydrator, a dehydrator having a belt-like filter for receiving a watercontaining powder and twin rolls between which the filter is sandwichedand compressed in a vertical direction.

[0037] (15) The method of operating a rotary hearth reducing furnaceaccording to (12) or (13) which is characterized by using, as thedehydrator, a centrifugal dehydrator having a vertically cylindricalwater containing powder holder the bottom of which is tapered inward anda screw-type powder discharge mechanism provided inside the holder inwhich the difference in rotation rate between the holder and the powderdischarge mechanism is 2 to 30 rotations per minute and the centrifugalforce exerted on the holder is 500G or more.

[0038] (16) The method of operating a rotary hearth reducing furnaceaccording to (12) or (13) which is characterized by dehydrating with theuse of, as the dehydrator, a dehydrator having a device for, from bothsides, pressing a filter holding a water containing powder with a forceof 10⁶N/m² or more.

[0039] (17) A method of operating a rotary hearth reducing furnace whichis characterized by feeding a cylindrical or circular shaped articlehaving a moisture content of 16 to 26% by mass, a thickness or diameterof 30 mm or less, and a powder filling rate of 0.43 to 0.58 and producedby compression-molding the mixture of a metal oxide-containing powderand a carbon-containing powder to a zone in the furnace the atmospherictemperature at which is 1170° C. or lower, and reducing the shapedarticle through calcination at temperatures of 1200° C. or higher.

[0040] (18) The method of operating a rotary hearth reducing furnaceaccording to (12), (13) or (17) which is characterized by using, as thecompression molding machine, an extrusion compression molding machineprovided with a device for pushing a wet powder and a hole from whichthe wet powder is extruded.

[0041] (19) The method of operating a rotary hearth reducing furnaceaccording to (12), (13), or (17) which is characterized by using, as thecompression molding machine, a briquette molding machine in which thewet powder is pressed against concavities provided on surfaces of twinrolls to be shaped.

[0042] (20) The method of operating a rotary hearth reducing furnaceaccording to (17) which is characterized by reducing the cylindrical orgranular shaped article having the thickness or diameter of 30 mm orless and produced by compression-molding the mixture of the metaloxide-containing powder and the carbon-containing powder.

[0043] (21) The method of operating a rotary hearth reducing furnaceaccording to (12), (13), or (17) which is characterized by, when an ironoxide-containing powder is employed as the metal oxide-containingpowder, reducing shaped articles the atomic molar weight of fixed carbonof which is 0.5 to 1.5 times the atomic molecular weight of oxygencombined with iron oxide.

[0044] (22) The method of operating a rotary hearth reducing furnaceaccording to (12), (13), or (17) which is characterized by feeding thecylindrical or granular shaped article formed by a compression moldingmachine to an area an atmospheric temperature at which is lower than theother areas inside the furnace for reducing through calcination.

[0045] (23) A shaped article of a raw material for use in a reducingfurnace which is characterized by being a cylindrical or granular shapedarticle of 30 mm or less formed by dehydrating a powdery mixturecontaining a metal oxide, carbon, and water to a moisture content of 15to 30% by mass relative to the whole mixture and thencompression-molding the mixture.

[0046] (24) A shaped article of a raw material for use in a reducingfurnace which is characterized by being a cylindrical or granular shapedarticle with a moisture content of 16 to 26% by mass, a thickness ordiameter of 30 mm or less, and a powder filling rate of 0.43 to 0.58obtained by compression-molding a mixture of a metal oxide-containingpowder and a carbon-containing powder.

[0047] (25) The shaped article of a raw material for use in a reducingfurnace according to (23) or (24) which is characterized in that, whenan iron oxide-containing powder is employed as the metaloxide-containing powder, the atomic molar amount of fixed carbon is 0.5to 1.5 times the atomic molar amount of oxygen combined with iron oxide.

[0048] The present invention relates to a rotary hearth reducing furnacefacility for effecting a reduction reaction with the use of amoisture-rich metal oxide containing powder as a raw material, a methodfor operating the same, and to a raw material for use in a reducingfurnace, and the present invention is carried out in the mannerdescribed below. The reduction process of a metal oxide according to therotary hearth method based on the present invention is illustrated inFIG. 1.

[0049] In a mixing vessel 1 as an apparatus for mixing a powdery rawmaterial which is in a moist-rich slurry condition well, the rawmaterial is stirred and mixed by a stirrer 2. The powdery raw materialis a mixture of a metal oxide-containing powder and a carbon-containingpowder. Examples of the metal oxide-containing powder include pelletfeed which is finely divided iron ore, and manganese or chromium ore ina powder form. Besides ores, electric arc furnace dusts, blast furnacegas sludge, basic oxygen furnace dusts, neutral sludge generated uponacid cleaning of iron products, powdery products generated in therefining or processing of metal such as mill scales resulted from thehot-rolling of steel, and others are also available. Moreover, as areducing agent, a carbon-based powder, such as oil coke, coke breeze,char, powdery coal, or any other fixed carbon-containing powder(hereafter, referred to as carbon powder) is mixed into the powdery rawmaterial.

[0050] When transporting the water-containing powdery raw materials froma plurality of tanks storing water-containing powders to the mixingvessel 1, it is desired that the metal oxide-containing powder isconveyed by a grab bucket crane or slurry transportation.

[0051] For evenly stirring the powdery raw material in a slurry statewithin a short period of time, the material needs to contain a largeamount of water. A variety of experiments performed by the inventorshave revealed that a high moisture content makes the mixing of thepowdery raw material smoother. That is, a high water content and itsconsequent high fluidity make the time taken to mix the raw materialhomogeneously shorter, resulting in a saving in power requiredtherefore. The inventors have also found that, with moisture content of100% or more relative to the total mass of the powders, the fluidity ofthe slurry becomes higher. In short, for making the mixing smoother, itis necessary to stir the mixture of a metal oxide-containing powder anda carbon-containing powder in such a condition as to have a moisturecontent of 100% or more relative to the total mass of the powders.

[0052] For preventing the powders from readily settling, it is preferredthat the particle size of each powder is small. By stirring stronger,the use of a powder of relatively large particle size is made possible.However, if the particle size of the metal oxide powder is 100 micronsand that of the carbon powder is 180 microns or smaller and thus themean particle size figured out with their mixing ratio taken intoaccount is 120 microns or less, at a moisture content of 100% by mass,it is made possible to homogeneously mix the slurry at a rate of,usually, about 10 to 30 rotations per minute.

[0053] The powdery raw material in a slurry state is sent by a slurrypump 3 to a dehydrator 4. In the dehydrator 4, the raw material isdehydrated to a moisture content of, relative to the mass of the powder,15 to 30%, preferably 16 to 23%. In the case of a powder of largeparticle size, it is relatively easy to adjust the water content to 16to 26% by mass, and an ordinary dehydrator, for example, a vacuumdehydrator, a press filter, a centrifugal decanter, or the like can beemployed. However, as described above, in the case of dehydration of aslurry constituted of such desirable powdery raw materials as those witha mean particle size of 120 microns or less, since dehydration to amoisture content of 30% by mass or less, preferably 20% by mass or lessby an ordinary dehydrator is difficult, a special dehydrator isemployed. Moreover, in some cases, several dehydrators of differenttypes are used in combination.

[0054] The facility is composed of a unit for pre-milling a rawmaterial, a unit for mixing a raw material, a granulating unit, apellet-drying unit, a rotary hearth reducing furnace, an exhaust gastreating unit, and a reduced pellet cooling unit.

[0055] What is important in the reduction of metal and that of dustsfrom steel manufacture is, as in the case of a rotary hearth reducingfurnace, an apparatus for pelletizing a raw material and a reducingagent. A unit for pretreating the raw material and a unit for bringingthe mixture of a powdery metal oxide raw material and a reducing agentinto a condition suitable for granulation are also important, andtherefore, the facility incorporated a variety of apparatuses forpre-milling the raw material or a ball mill for kneading.

[0056] As the dehydrator for the case of the use of a microfine powder,a dehydrator illustrated in FIG. 3 is suitable, and it includes a filter23 for receiving a slurry and twin rolls 25 between which the filter issandwiched. In the dehydrator, a slurry 26 is cast on the filter 23incorporated therein like an endless belt, and the filter is thensandwiched between the compression twin rolls 26 for dehydration. If themoisture content of the slurry is high, pre-dehydration of the slurry infront of the compression twin rolls 26 by a vacuum suction apparatus 24provided under the filter will facilitate an efficient dehydration.

[0057] Moreover, as a dehydrator for the case of an extraordinarily finepowder, the use of a vertical centrifuge is also effective. Thiscentrifuge is a centrifugal dehydrator including a cylindrical slurryholder the bottom of which is tapered inward and a screw-type powderdischarge mechanism inside the holder. The difference in rotation ratebetween the slurry holder and the powder discharge mechanism is 2 to 30rotations per minute, and the centrifugal force exerted on the slurryholder is 500G or more. Although the performance of a single dehydratoritself is not so high, due to the centrifugal force, its separationefficiency is good and this dehydrator is suitable for the dehydrationof a moisture-rich fine powder. Particularly, it is effective to adoptthis dehydrator for the dehydration of a powder the particle size ofwhich is as small as several microns to 30 microns or several microns to40 microns.

[0058] Furthermore, it is also possible to use, as the dehydrator, ahigh pressure press dehydrator including a device for pressing theslurry-receiving filter from both sides with a force of 10⁶N/m² orgreater. However, as compared with the above-mentioned dehydratorequipped with twin rolls, it is inferior in dehydration performance andtherefore it is preferred to be employed for the case of relativelycrude powders having a particle size of 100 microns or so.

[0059] Thereafter, the wet powder dehydrated to a moisture content of 15to 30% by mass, preferably 16 to 26% by mass is conveyed to acompression molding machine 6 by a sludge transporting conveyer 5, atwhich the powder is shaped. Examples of the compression molding machineinclude, typically, a molding machine of the type shown in FIG. 4 inwhich a wet powder is pressed into holes (hereafter, referred to as ahole-type pelleter) and a briquette molding machine illustrated in FIG.5 in which a wet powder is pressed against the concavities provided onthe twin rolls.

[0060] In the hole-type pelleter, as shown in FIG. 4, the wet materialis extruded from the holes in the form of cylinders. The raw material isfed from a raw material feeding port 28 and pressed into a number ofholes 34 provided on a bottom plate 33 by a roller 32 driven by adriving device 29, a drive power transmitting mechanism 30, and adriving shaft 31 to be shaped into shaped articles 35. As a pelleteremploying a different mechanism, there can be mentioned a pelleter ofthe type including a screw-type pressing mechanism in its body withwhich the material is pressed against a plate provided with holes. Thebriquette molding machine is such an apparatus as is illustrated in FIG.5, in which a powder is fed from a raw material feeding part 36 andcompression-molded by rollers 37 provided with concavities 38.

[0061] The reason why these types of molding machines are selected isthat they can provide shaped articles satisfying the requirements. Twomain characteristics that the shaped articles are required to have arebeing free from explosive cracking in the furnace and high dropresistance in their wet condition.

[0062] The pan pellet production method, which is a conventional moldingmethod, is a method in which shaped articles are grown by rolling apowder on a slope to provide new powder layers thereon. The powderfilling rate of the pellets produced according to this method is as highas about 0.65 to 0.75, showing it is the very dense shaped article. Thedense shaped articles tend to crack explosively at an area of 900° C. orhigher in the raw material feeding part of the rotary hearth. If thediameter of the pellets is about 10 mm and the moisture content is 3% bymass or higher, the pellets explosively crack as soon as they are fed tothe furnace. Incidentally, the powder filling rate is the rate of thepowder volume contained in the volume of a shaped article.

[0063] The inventors have repeatedly made experiments on the conditionsunder which explosive-cracking of wet shaped articles directly fed tothe furnace is caused, and finally have found that, for preventing theexplosion-cracking of shaped articles, it is important that the powderfilling density of the shaped articles is relatively low. That is, thecause of explosive-cracking in a reducing furnace with a rotary hearthis that the shaped articles are supplied to the furnace heated up to ashigh as 900° C. or higher and water contained therein quicklyevaporates, resulting in a rise in the internal pressure of the shapedarticles. The inventors of the present invention performed a variety ofexperiments and finally have found that the explosive-crackingphenomenon is greatly influenced by both the powder filling density andthe moisture content of the shaped articles. Incidentally, the powderfilling rate is the percentage of the powder occupying inside of ashaped article.

[0064] Moreover, they have found that, even if their moisture 22 contentis high, a reduction in powder filling rate makes the shaped articlesless explosive. For preventing the internal pressure of the shapedarticles from being raised upon quick evaporation of the moisturecontained therein, the existence of many gaps between the particlesconstituting the powder is important. A decrease in powder filling rateled to an increase in explosive-cracking marginal moisture content, anda powder filling rate of 0.58 or less did not cause theexplosive-cracking phenomenon even with a moisture content of 16 to 26%.However, if the powder filling rate is too low, the drop resistance isdeteriorated, so that it is necessary to ensure a powder filling rate of0.4 or higher.

[0065] Generally, the production of shaped articles according to acompression molding method has the advantage that shaped articlesproduced thereby have a low powder filling rate being a condition forless-explosiveness. For preventing the internal pressure of the shapedarticles from being raised upon quick evaporation of the moisturecontained therein, the existence of many gaps between the particlesconstituting the powder is important.

[0066]FIG. 6 shows the influence that the powder filling rate exerts onthe explosive-cracking marginal moisture content when shaped articleshaving a diameter of 20 mm are fed to an atmosphere of 1170° C. If thepowder filling rate decreases, the explosive-cracking marginal moisturecontent increases. When the powder filling rate was 0.58 or less, evenwith a moisture content of 18% by mass, neither explosive-cracking norpartial powdering occurred. A moisture content of 23 to 26% by mass ledto the surface peeling phenomenon, but explosive-cracking did not occur.Moreover, in the case of a powder filling rate of 0.55 or less, evenwith a moisture content of 23 to 30% by mass or so, the surface peelingphenomenon did not occur. That is, in view of the prevention ofexplosive-cracking, it is desired that the powder filling rate is 0.58or less. The explosive-cracking marginal moisture content of shapedarticles with a low powder filling rate shows a tendency to keep levelat 23 to 26% by mass.

[0067] Furthermore, the inventors have found that the conditions underwhich the explosive-cracking phenomenon occurs are different fordifferent shaped article, depending on the shape thereof. Firstly, evenif their powder filling rate was 0.58, tile-shape articles 20 mm inthickness and 150 mm in length and width explosively cracked at amoisture content of 17%. On the other hand, despite their having apowder filling rate of 0.58, cylindrical shaped articles having adiameter of 15 mm and a length of 25 mm produced by a hole-type pelleterdid not explode until their moisture content reached 25%. Moreover, 20mm thick almond shape articles having a powder filing rate of 0.58 and aside of 40 mm and produced by a briquette molding machine were free fromexplosive-cracking up to a moisture content of 23%. That is, in contrastto plate shape articles that easily explode, cylindrical or granularshaped articles are less susceptible to explosive-cracking. Thus, in thepresent invention, the shape of the shaped articles is specified ascylindrical or granular.

[0068] The reason why shaped articles produced by a hole-type pelleteror briquette molding machine are less explosive was also made clear. Thesurface of a cylindrical shaped article formed by a hole-type pelleteris smooth, but its cross section is rough. As a result, even with a highmoisture content, since the passing resistance of water vapor is low,explosive-cracking is inhibited from occurring. Under certainconditions, even with a moisture content of 26% by mass, shaped articlesproduced by a hole-type pelleter did not explode in a furnace of 1170°C., proving them to be most excellent in explosion resistance. Even ifshaped by a briquette molding machine, since the thickness of the rawmaterial is compressed, the density of sides of the briquette shapedarticle does not rise, consequently allowing water vapor to be readilydischarged therefrom. Moreover, the inventors have found that theexplosiveness of shaped articles is influenced by their sizes. Even inthe case of cylindrical or granular shaped articles, under certainconditions, if the size is 30 mm or more, they explosively crack in thefurnace of 1170° C. in spite of their moisture content of 26% by mass.Therefore, it is desired that the thickness or diameter of the shapedarticles is 30 mm or less.

[0069] In a reducing furnace of the rotary hearth-type, acenter-lacking-disk-shape hearth rotates. The hearth passes through acalcination/reducing zone and, in the zone at which shaped articles aredischarged, reduced shaped articles are discharged. Thereafter, thehearth arrives to a shaped article supplying part. From the fact thatthe temperature of the hearth at this point of time is 1150 to 1300° C.,it can be seen that, in a normal operation, the temperature of theshaped article supplying part is 1000 to 1250° C. That is, under certainoperation conditions, the temperature of the shaped article supplyingpart can be 1170° C. or higher. In this case, it is preferred that thetemperature is adjusted to 1170° C. or lower by cooling the shapedarticle supplying part. For cooling the shaped article supplying part,it is recommended to provide a water cooling wall as the ceilingsurrounding the shaped article supplying part or design the shapedarticle supplying part so as to be protected from a high temperaturecombustion gas flowing into it.

[0070] Secondly, the important characteristic the shaped articles arerequired to have is a high drop resistance. In the course of conveyancefrom the molding machine to the hearth, when passed from one conveyer toanother conveyer and fed to the hearth, the shaped articles are droppedseveral times by a distance of about 0.5 to 2 m. Therefore, they arerequired to be high in drop resistance (expressed by the total dropdistance taken to spoil the shape of the shaped articles). In the caseof a rotary hearth reducing furnace, a value of about 4 to 5 meters ormore is required. That the drop resistance of shaped articles having alow powder filling rate is generally low is incompatible with the abovedescribed conditions under which explosive-cracking is inhibited fromoccurring. The inventors made studies to improve the drop resistance ofshaped articles with a low powder filling rate and have found that, iftheir moisture content is of a certain value or higher, even if droppedand impacted, the shaped articles are not broken and are only distorted.

[0071] The studies on the influence of the moisture content on the dropresistance the inventors made have revealed that, with a moisturecontent of 16% by mass or more, the drop resistance of shaped articleshaving a powder filling rate of not less than 0.43 will be 4.2 meters ormore. However, when the powder filling rate was 0.43 or less, regardlessof its moisture content, the drop resistance was as low as 2 to 4 metersor so. Thus, for assuring a suitable drop resistance, it is desired thatthe moisture content is 16% by mass or more and the powder filling rateis 0.43 or more.

[0072] Moreover, even with the same moisture content or powder fillingdensity as that mentioned above, the above described shaped articles inthe form of tiles were broken by just a single fall from the height of0.5 m. That is, it can be seen that, due to their shape, the dropresistance of tile-shape articles produced according to the methodrecited in Japanese Patent Laid-Open Publication No. Hei. 11-12624 istoo low to allow the shaped articles to be fed to the furnace as theyare if handled in a normal manner. In contrast to these shaped articles,those produced in accordance with the present invention were, even ifhandled in a normal manner, susceptible of being fed to the furnace asthey were.

[0073] Based on the results of the experiments described above, theinventors have found that, as the requirements of the shaped articles,it is desired that the moisture content falls within the range of 15 to30% by mass, preferably 16 to 26% by mass and the powder filling rate isin the range of 0.43 to 0.58, and that the above mentioned hole-typepelleter and the briquette molding machine are the most effectiveapparatuses. Although it is possible to produce shaped articles thatmeet the object of the present invention by other devices, the hole-typepelleter and briquette molding machine produce shaped articles of highperformance at low cost and therefore are the most effectiveapparatuses.

[0074] The shaped articles formed according to the method describedabove are, in their as-wet condition, supplied to a rotary hearthreducing furnace 9 by a swing conveyer 8 via a shaped articletransporting conveyer 7, the swing conveyer 8 being a shaped articlesupplying device. The temperature of the shaped article supplying partof the rotary hearth reducing agent 9 is 1170° C. or lower.

[0075] In the rotary hearth-type reducing furnace 9, the wet shapedarticles are fed to a zone the atmospheric temperature at which is 1170°C. or lower. If the atmospheric temperature is 1170° C., even thoseproduced under such conditions as are specified in the present inventionmay explode, for the pace of increase in the internal temperature of theshaped articles is so high that the water vapor pressure gets high.Therefore, the temperature of this zone needs to be 1170° C. or lower.

[0076] In the rotary hearth reducing furnace 9, the shaped articles arecalcined at about 1100 to 1350° C., and the metal oxide is reduced bycarbon contained in the shaped articles. Since the raw material isstirred and mixed in a moisture-rich condition and therefore the metaloxide and carbon contained in the shaped articles formed therefrom arehomogeneously mixed, the raw material mixing method of the presentinvention has the effect of helping the reaction to be carried outefficiently.

[0077] Furthermore, the inventors have found the importance ofcontrolling the ratio of carbon in the reduction of iron oxide. Whenreducing iron oxide, if the amount of carbon is insufficient, in somecases, the reduction is not effected completely, resulting in a decreasein the degree of metallization. Moreover, if the amount of carbon isexcessive, excess carbon reacts with iron to form cementite (Fe₃C) and,at 1200° C. or so, the reduced shaped articles start melting in thefurnace. Since the hearth or discharging device of an ordinary rotaryhearth reducing furnace is not designed for molten iron, if iron melts,there arises the problem that the hearth is damaged.

[0078] If the amount of fixed carbon contained in the shaped articles is1.5 times or less the molar number of fixed carbon figured out on theassumption that it reacts with oxygen combined with iron oxide toproduce carbon monoxide (hereafter, referred to as calculated molaramount of carbon), the above mentioned problems of incomplete reductionand molten iron do not occur. Moreover, the inventors have found that inthe reaction among the reaction to produce carbon monoxide and thereaction to produce carbon dioxide, 10 to 70% of the carbon atomsreactive with iron oxide are reacted to produce carbon dioxide though itchanges for different conditions. As a result, if the amount of fixedcarbon is half the calculated carbon molar amount or more, there can beobtained reduction products the degree of metallization of which is 70%or higher.

[0079] When the amount of fixed carbon is half the calculated carbonamount, the degree of metallization of iron is about 80% and thereforethe resulting product is somehow susceptible of direct use as reducediron. On the other hand, in the case where the amount of fixed carbon is1.5 times the calculated carbon amount, the degree of metalization is ashigh as 97%. The amount of residual carbon was about 2.5% relative tothe amount of reduced iron at this time. Accordingly, even if the wholeresidual carbon has been carburized with iron, the melting point of theresulting product is kept at 1300° C. or higher. Therefore, in therotary hearth reducing furnace the internal temperature of which is, atthe highest, about 1300° C., the problem that the reduced product meltsdoes not occur.

[0080] The reduced shaped articles are discharged from the rotary hearthreducing furnace 9 and cooled to normal temperature in a product coolingdevice 13. However, in the case of use in an electric arc furnace or thelike, the shaped articles the temperature of which is as high as 900° C.may be subjected to a melting step as they are. Via a gas cooling device10 and a dust collector 11, exhaust gas generated upon combustion in therotary hearth reducing furnace 9 is exhausted to atmosphere through achimney 12.

[0081] Incidentally, the shaped articles of raw materials for use in arotary hearth reducing furnace need only be cylindrical or granular onesthat are produced by compression-molding the mixture of a metaloxide-containing powder and a carbon-containing powder and have a watercontent of 15 to 30% by mass, preferably 16 to 26% by mass, a powderfilling rate of 0.43 to 0.58, and a thickness or diameter of 30 mm orless, and they are not necessarily required to be produced in accordancewith the process described above. Even with those produced by adifferent technique, if they satisfy the requirements, the reduction canbe effected in such a manner as to meet the object of the presentinvention.

[0082] Application of the present invention to the treatment of sludgeor dusts generated in the refining or processing of metal isparticularly effective. For example, the gas ash from the blast furnaceof a steel plant is collected by a wet-type venturi scrubber and madeinto a slurry by a thickener. Moreover, there are neutralized sludge ofcorrected waste acid generated in the acid cleaning. Such dusts orsludge are processed by a dehydrator. However, in addition to the factthat it is difficult to recycle them, their recycle is costly. Forexample, by directly sending these dusts or sludge from the thickener tothe mixing vessel 1, it is made possible to produce, without anintermediate treatment, shaped articles of raw materials for reductionwith ease. Accordingly, the use of dusts or sludge generated in thecourse of metal refining or processing is one of the most desirablemethods in the present invention.

[0083] For comparison of the operation methods, a facility employed in aconventional method is shown in FIG. 2. In the conventional facility,after the dehydration step in the case of operation by the facility ofthe present invention, the raw material is conveyed by a sludgy powdertransporting conveyer 15 to a powder dryer 16, at which the raw materialis dried to a moisture content of 5 to 10% by mass. Then, while addingwater to the powder by a water sprinkler 18, the raw material ispelletized by a granulator 17. The resulting pellets are sent to apellet dryer 20 by a pellet transporting conveyer 19, at which they aredried to a moisture content of about 2% by mass. Thereafter, the pelletsare reduced through calcination by a rotary hearth reducing furnace. Ascan be understood from the above, the operation by a conventional methodincludes many steps and its process is complicated as compared with thatof the present invention. In addition, a large amount of energy isconsumed in a series of moisture controlling steps of dehydration,drying, hydration, and dehydration, proving the facility according tothe present invention to be effective in comparison with the operationby a conventional method. From the view point of the raw material to beused in the rotary hearth reducing furnace, the present inventionprovides a technique for producing reduction-use shaped articles from awet raw material in the easiest manner. As for the requirements, it ispreferred that the shaped articles which are produced by a compressionmolding machine are cylindrical or granular and have a thickness ordiameter of 30 mm or less, a moisture content of 15 to 30% by mass,preferably 16 to 26% by mass, and a powder filling rate of 0.43 to 0.58.By reducing the shaped articles formed according to the processdescribed above, there are obtained shaped articles of raw materialswhich are, due to their high drop resistance and non-explosiveness,economically reducible by a rotary hearth reducing furnace.

BRIEF DESCRIPTION OF THE DRAWINGS

[0084]FIG. 1 shows one embodiment of the structure of a rotary hearthreducing furnace for reducing a water containing powdery raw materialbased on the present invention.

[0085]FIG. 2 shows one embodiment of the structure of a rotary hearthreducing furnace based on a conventional method.

[0086]FIG. 3 shows a dehydrator of the type in which a slurry is cast onan endless belt filter and compressed by compression twin rolls.

[0087]FIG. 4 shows a compression molding machine of the type in which apowder is extruded from its holes. The left is a schematic view and theright illustrates compression rollers.

[0088]FIG. 5 shows a briquette compression molding machine of the typein which a powder is compression-molded in its concavities.

[0089]FIG. 6 is a graph showing the influence the powder filling rate ofthe shaped article exerts on the explosive-cracking marginal moisturecontent at 1170° C.

[0090]1: mixing vessel 2: stirrer 3: slurry pump 4: dehydrator 5: sludgetransporting conveyer 6: compression molding machine 7: shaped articletransporting conveyer 8: swing conveyer 9: rotary hearth reducingfurnace 10: gas cooling device 11: dust collector 12: chimney 13:product cooling device 14: dehydrator 15: sludgy powder transportingconveyer 16: powder dryer 17: granulator 18: water sprinkler 19: pellettransporting conveyer 20: pellet dryer 21: dry pellet conveyer 22:slurry port 23: filter 24: vacuum suction apparatus 25: compression twinrolls 26: slurry 27: dehydrated product 28: raw material supplying port29: driving device 30: driving force transmitting mechanism 31: drivingshaft 32: roller 33: bottom plate 34: holes 35: shaped article 36: rawmaterial supplying part 37: compression rollers 38: concavities 39:briquettes

BEST MODE FOR CARRYING OUT THE INVENTION

[0091] Examples in which operations were carried out in accordance withthe present invention are shown in Table 1. The facility employed is onethat is illustrated in FIG. 1, the reduction performance of which is, interms of the amount of wet shaped articles, 10 tons per hour. As thedehydrator, a dehydrator of the twin roll-type was employed, and ahole-type pelleter was used as the molding machine.

EXAMPLES 1 AND 2

[0092] As shown in Table 1, two types of raw materials: the mixture ofpellet feed being microfine powdery ore and coke breeze of 1 mm or less;and the mixture of blast furnace gas sludge from a plant ofthrough-steel manufacture, sedimentary sludge of scale pit generated bythe hot rolling, and coke breeze of 1 mm or less were employed. TABLE 1Example 2 Blast furnace gas sludge Raw material (iron Example 1 Scalepit source) Unit Pellet feed sedimentary sludge FeO % 1.2 10.5 Fe₂O₃ %80.3 58.3 C % 12.5 10.2 ZnO % 0.01 0.95 Na % 0.12 0.25 K % 0.03 0.33 Rawmaterial shaped article Moisture content of % 130 185 slurry Moisturecontent of % 17.1 19.8 shaped article Powder filling rate 0.57 0.55 Dropresistance of m 4.7 6.9 shaped article Conditions of reducing furnaceTemperature of raw ° C. 981 983 material supplying part Reducingtemperature ° C. 1210 1210 Reducing time min 15 15 Product Degree of %95.2 92.8 metallization Degree of dezincing % 89.2 97.3 Degree of % 97.899.1 dealkalization Agglomerate production % 93.8 95.4 yield

[0093] The operation conditions are as shown in Table 1. The moisturecontent of the raw material in the mixing vessel 1 is 130 to 185%relative to the mass of the powder, and that of the raw material beforemolding is 17 to 20% relative to the mass of the powder. The powderfilling rate is within the range specified in the present invention. Thediameter and length of each shaped article are 15 mm and 25 mm,respectively. The furnace temperature of the shaped article supplyingpart is about 980° C. The furnace temperature of the reduction zone is1210° C. Moreover, the reduction time is 15 minutes.

[0094] Example 1 is the case of an operation which used pellet feed.Since the carbon mixing ratio was appropriate, its productivity washigh. The operation was performed at a degree of metallization of ashigh as 97% and was substantially free from powdering due to a fall andexplosive-cracking, so that its agglomerate production yield was as highas 94%. Example 2 is the case of operation with the use of blast furnacegas sludge and sedimentary sludge of scale pit generated by the hotrolling, aiming at not only reduction but also dezincification anddealkalization. In this operation, the degree of metallization was 91%,the degree of dezincification was 97.5%, and the degree ofdealkalization was 99%. As can be seen from these figures, impuritieswere effectively eliminated. This case was also substantially free frompowdering due to a fall and explosive-cracking, so that its agglomerateproduction yield was as high as 95%.

[0095] The reduction according to the present invention and thataccording to a conventional method employing the facility as illustratedin FIG. 2 were compared from an economical viewpoint. In the operationof the present invention, since the pretreatment of the raw material iscomposed only of a mixing step, a dehydration

[0096] step, and a molding step, the cost of pretreatment of the rawmaterial does not exceed approximately 30% of that in the comparativeexample. Moreover, the present invention provides a saving of about 15%in the amount of money cost throughout the process. Furthermore, inExamples, as compared with the comparative example, the constructioncost was reduced by about 10%, because the pretreatment in the presentinvention is simpler than that in the comparative example.

[0097] As described above, the rotary hearth reducing furnace facilityemploying a wet powder according to the present invention is free fromsuch operation related problems as explosive-cracking of shaped articlesof raw materials. The construction cost of this facility is low, and itis possible to operate the facility a t low cost, including savings inenergy consumption and other operation related costs. Moreover, the costof maintenance of the facility according to the present invention is lowand the facility enables a metal oxide to be reduced economically.Particularly, since it is possible to omit a powder drying step and adevice used therein, its effect of reducing the equipment cost is great.

EXAMPLES 3, 4

[0098] As the raw materials, as shown in Table 2, two types of mixtureswere employed, one of which is the mixture of pellet feed being amicrofine powdery ore and coke breeze of 1 mm or less and the other isthe mixture of blast furnace gas sludge from a through-steelmanufacturing plant, sedimentary sludge of scale pit generated by thehot rolling, and coke breeze of 1 mm or less. TABLE 2 Example 4 Blastfurnace gas sludge Raw material (iron Example 3 Scale pit source) UnitPellet feed sedimentary sludge FeO % 1.2 10.5 Fe₂O₃ % 80.3 58.3 C % 12.510.2 ZnO % 0.01 0.95 Na % 0.12 0.25 K % 0.03 0.33 Raw material shapedarticle Moisture content of % 130 185 slurry Moisture content of % 17.119.8 shaped article Powder filling rate 0.57 0.55 Drop resistance of m4.7 6.9 shaped article Conditions of reducing furnace Temperature of raw° C. 981 983 material supplying part Reducing temperature ° C. 1210 1210Reducing time min 15 15 Product Degree of % 95.2 92.8 metallizationDegree of dezincing % 89.2 97.3 Degree of % 97.8 99.1 dealkalizationAgglomerate production % 93.8 95.4 yield

[0099] The operation conditions are as shown in Table 2. The moisturecontent of the raw material in the mixing vessel 1 is 120 to 200% of themass of the powder, and that of the raw material before molding is 17 to20% of the mass of the powder. The powder filling rate is within therange specified in the present invention. The diameter and length ofeach shaped article are 15 mm and 25 mm, respectively. The furnacetemperature of the shaped article supplying part is about 980° C. Thefurnace temperature of the reduction zone is 1210° C. Moreover, thereduction time is 15 minutes.

[0100] Example 3 is the case of an operation which used pellet feed.Since the carbon mixing ratio was appropriate, its productivity washigh. The operation was performed at a degree of metallization of ashigh as 97% and was substantially free from powdering due to a fall andexplosive-cracking, so that its agglomerate production yield was as highas 94%. Example 4 is the case of operation with the use of blast furnacegas sludge and sedimentary sludge of scale pit generated by the hotrolling, aiming at not only reduction but also dezincification anddealkalization. In this operation, the degree of metallization was 91%,the degree of dezincification was 97.5%, and the degree ofdealkalization was 99%. As can be seen from these figures, impuritieswere effectively eliminated. This case was also substantially free frompowdering due to a fall and explosive-cracking, so that its agglomerateproduction yield was as high as 95%.

[0101] The reduction according to the present invention and thataccording to a conventional method employing the facility as illustratedin FIG. 2 were compared from an economical viewpoint. In the operationof the present invention, since the pretreatment of the raw material iscomposed only of a mixing step, a dehydration step, and a molding step,the cost of pretreatment of the raw material does not exceedapproximately 30% of that in the comparative example. Moreover, thepresent invention provides a saving of 15% in the amount of money costthroughout the process.

[0102] As described above, the operation with the use of a wet powderaccording to the present invention is free from such operation relatedproblems such as explosive-cracking of shaped articles of raw materials.The construction cost of this facility is low, and it is possible tooperate at low cost, including savings in energy consumption and otheroperation related costs. As a result, reduction of ores and powders suchas metal oxide-containing dusts or sludge by a rotary hearth reducingfurnace was economically carried out.

INDUSTRIAL APPLICABILITY

[0103] According to the present invention, in a rotary reducing furnacemethod, with the use of a wet powdery raw material, it is possible toeffect the reduction of a metal oxide thereby to produce a metal.Moreover, the present invention is effective in economically treatingmetal oxide-containing dusts or sludge generated by the metalmanufacturing industry, and reduction of a moisture-rich metal oxidecontaining powder or treatment of metal oxide-containing dusts or sludgegenerated in the process of metal refining or processing areeconomically effected through a small number of steps by a facility forreducing a metal oxide, incorporating a rotary hearth reducing furnace.The operation by the present invention is particularly effective intreating dusts or sludge containing a large amount of moisture.

1. A facility for reducing a metal oxide, characterized by comprising acompression molding machine for shaping a mixture of a water containingpowder containing metal oxide and a powder containing carbon into acylindrical or granular shaped article; a shaped article transportingconveyer; a shaped article feeding device; and a rotary hearth reducingfurnace, wherein these are placed in this order and connected to eachother by transporting means.
 2. A facility for reducing a metal oxide,characterized by comprising a device for mixing a powder containingmetal oxide and a carbon-based powder in a water containing condition; aslurry transporting device; a dehydrator; a compression molding machinefor producing a cylindrical or granular shaped article; a shaped articletransporting conveyer; a shaped article feeding device; and a rotaryhearth reducing furnace, wherein these are placed in this order andconnected to each other by a transporting means.
 3. The facility forreducing a metal oxide according to claim 2, characterized by using, asthe dehydrator, a dehydrator having a belt-like filter for receiving thewater containing mixture of a metal oxide-containing powder and acarbon-based powder; and twin rolls between which said filter issandwiched and compressed.
 4. The facility for reducing a metal oxideaccording to claim 2, characterized by using, as the dehydrator, acentrifugal dehydrator having a vertically cylindrical slurry holder abottom of which is tapered inward and a screw-type powder dischargemechanism provided inside the holder, wherein the difference in rotationrate between said slurry holder and said powder discharge mechanism is 2to 30 rotations per minute, and the centrifugal force exerted on saidslurry holder is 500G or more.
 5. The facility for reducing a metaloxide according to claim 2, characterized by using, as the dehydrator, adehydrator having a device for, from both sides, pressing a filter forreceiving the mixture of the powder containing the metal oxide and thepowder containing carbon in their water containing condition with aforce of 10⁶N/m² or more.
 6. The facility for reducing a metal oxideaccording to claim 1 or 2, characterized by using, as the moldingmachine, a compression molding machine of a type which extrudes a wetpowder from holes each having a diameter of 30 mm or less.
 7. Thefacility for reducing a metal oxide according to claim 1 or 2,characterized by using, as the molding machine, a briquette moldingmachine a maximum thickness of each concavity of which is 30 mm or less.8. The facility for reducing a metal oxide according to claim 1 or 2,characterized in that, in the course of transportation from a shapedarticle manufacturing machine to a hearth of a rotary furnace, a totaldrop distance of the shaped article is 4.1 m or less.
 9. The facilityfor reducing a metal oxide according to claim 1 or 2, characterized byusing, as the shaped article feeding device, a swing-type belt conveyeror a vibration feeder.
 10. The facility for reducing a metal oxideaccording to claim 2, characterized in that the powder containing themetal oxide and the carbon-based powder are supplied to the device formixing from a plurality of tanks storing water-containing powders by agrab bucket crane and/or slurry transportation in such a condition as tohave a moisture content of 100% or higher relative to the total mass ofthe powders.
 11. The facility for reducing a metal oxide according toclaim 1 or 2, characterized by comprising a mechanism for controlling anatmospheric temperature of a shaped article supplying zone in the rotaryhearth reducing furnace so as to be 1170° C. or lower.
 12. A method ofoperating a rotary hearth reducing furnace, characterized by dehydratinga powdery mixture containing a metal oxide, carbon, and water to amoisture content of 15 to 30% by mass relative to the whole mixture;shaping said mixture into a plurality of cylindrical or granular shapedarticles by compression molding; and directly feeding the resultingshaped articles to the reducing furnace for reducing throughcalcination.
 13. A method of operating a rotary hearth reducing furnace,characterized by feeding a shaped article having a powder filling rateof 0.43 to 0.58 produced by mixing a powder containing metal oxide andcarbon in such a condition as to have a moisture content of 100% orhigher relative to the total powder mass, dehydrating the mixture by adehydrator to a moisture content of 16 to 26% by mass, and shaping themixture by a compression molding machine to a zone in the furnace theatmospheric temperature at which is 1170° C. or lower, and then reducingthe shaped article through calcination at temperatures of 1200° C. orhigher.
 14. The method of operating a rotary hearth reducing furnaceaccording to claim 12 or 13, characterized by using, as the dehydrator,a dehydrator having a belt-like filter for receiving a water containingpowder and twin rolls between which said filter is compressed in avertical direction.
 15. The method of operating a rotary hearth reducingfurnace according to claim 12 or 13, characterized by using, as thedehydrator, a centrifugal dehydrator having a vertically cylindricalwater containing powder holder a bottom of which is tapered inward and ascrew-type powder discharge mechanism provided inside the holder inwhich a difference in rotation rate between said holder and said powderdischarge mechanism is 2 to 30 rotations per minute and a centrifugalforce exerted on the holder is 500G or more.
 16. The method of operatinga rotary hearth reducing furnace according to claim 12 or 13,characterized by dehydrating with the use of, as the dehydrator, adehydrator having a device for, from both sides, pressing a filterholding a water containing powder with a force of 10⁶N/m² or more.
 17. Amethod of operating a rotary hearth reducing furnace, characterized byfeeding a cylindrical or circular shaped article having a moisturecontent of 16 to 26% by mass, a thickness or diameter of 30 mm or less,and a powder filling rate of 0.43 to 0.58 and produced bycompression-molding a mixture of a metal oxide-containing powder and acarbon-containing powder to a zone in the furnace the atmospherictemperature at which is 1170° C. or lower, and reducing the shapedarticle through calcination at temperatures of 1200° C. or higher. 18.The method of operating a rotary hearth reducing furnace according toclaim 12 or 17, characterized by using, as the compression moldingmachine, an extrusion compression molding machine provided with a devicefor pushing a wet powder and a hole from which the wet powder isextruded.
 19. The method of operating a rotary hearth reducing furnaceaccording to claim 12, 13, or 17, characterized by using, as thecompression molding machine, a briquette molding machine in which thewet powder is pressed against concavities provided on surfaces of twinrolls to be shaped.
 20. The method of operating a rotary hearth reducingfurnace according to claim 17, characterized by reducing the cylindricalor granular shaped article having a thickness or diameter of 30 mm orless and produced by compression-molding the mixture of the metaloxide-containing powder and the carbon-containing powder.
 21. The methodof operating a rotary hearth reducing furnace according to claim 12, 13,or 17, characterized by reducing the shaped article an atomic molaramount of fixed carbon of which is 0.5 to 1.5 times an atomic molaramount of oxygen combined with iron oxide when an iron oxide-containingpowder is employed as the metal oxide-containing powder.
 22. The methodof operating a rotary hearth reducing furnace according to claim 12, 13,or 17, characterized by feeding the cylindrical or granular shapedarticle formed by a compression molding machine to a zone an atmospherictemperature at which is lower than the other areas inside the furnace,and reducing it through calcination.
 23. A shaped article of a rawmaterial for use in a reducing furnace, characterized in that the shapedarticle is a cylindrical or granular shaped article of 30 mm or lessformed by dehydrating a powdery mixture containing a metal oxide,carbon, and water to a moisture content of 15 to 30% by mass relative tothe whole mixture and then compression-molding said mixture.
 24. Ashaped article of a raw material for use in a reducing furnace,characterized in that the shaped article is a cylindrical or granularshaped article with a moisture content of 16 to 26% by mass, a thicknessor diameter of 30 mm or less, and a powder filling rate of 0.43 to 0.58obtained by compression-molding a mixture of a metal oxide-containingpowder and a carbon-containing powder.
 25. The shaped article of a rawmaterial for use in a reducing furnace according to claim 23 or 24,characterized in that an atomic molar amount of fixed carbon is 0.5 to1.5 times an atomic molar amount of oxygen combined with iron oxide whenan iron oxide-containing powder is employed as the metaloxide-containing powder.